Nesse trabalho, é investigada a combustão pré-misturada de metano e ar em um queimador poroso radiante com área de seção transversal variável. A estabilidade de chama e a eficiência de radiação neste tipo de queimador são analisadas através de simulação numérica. O problema considerado para análise é de um queimador unidimensional de área variável com perdas de calor por radiação em suas extremidades. A metodologia numérica usada para resolver o conjunto de equações de conservação é o método dos volumes finitos com o sistema de coordenadas cartesianas. Os resultados mostram que, o aumento da área da seção transversal proporciona um aumento na faixa de estabilidade de chama do queimador quando comparado com um de área constante. A eficiência de radiação também é influenciada positivamente pela variação de área, ou seja, um aumento na área da seção de saída do dispositivo resulta em um aumento na eficiência. Também é testada uma modelagem alternativa baseada no método de curvas de nível (level-set method). Nesse modelo as equações das espécies químicas são substituídas pela equação-G, a qual descreve a dinâmica de uma frente de chama infinitamente fina. Os resultados numéricos das simulações bem como as vantagens e as limitações do modelo de curvas de nível são discutidas. Em linhas gerais os resultados do modelo de curvas de nível não foram capazes de reproduzir adequadamente o comportamento obtido com o modelo convencional. / In this work, the premixed combustion of methane and air in a porous radiant burner with a variable cross-sectional area is investigated. The flame stability and the radiant efficiency in this kind of burner are analyzed through numerical simulation. The problem considers a variable area one-dimensional burner with radiation heat losses in its extremities. The numerical method used to solve the set of conservation equations is the finite volume method with the Cartesian coordinate system. The results show that an increase of the cross-sectional area promotes an increase of the flame stability range when compared with a constant area burner. The radiant efficiency is also positively influenced by the area variation, i.e., the increase of the outlet area results in an enhanced efficiency. An alternative modelling based on the level-set method is also tested. In this model the equations of chemical species are replaced by the G-Equation, which describes the dynamics of an infinitely thin flame front. The numerical results of simulations as well as advantages and limitations of the level-set model are discussed. In general the results of the level-set model were not able to reproduce in a suitable way the behavior obtained with the conventional model.

Nesse trabalho, é investigada a combustão pré-misturada de metano e ar em um queimador poroso radiante com área de seção transversal variável. A estabilidade de chama e a eficiência de radiação neste tipo de queimador são analisadas através de simulação numérica. O problema considerado para análise é de um queimador unidimensional de área variável com perdas de calor por radiação em suas extremidades. A metodologia numérica usada para resolver o conjunto de equações de conservação é o método dos volumes finitos com o sistema de coordenadas cartesianas. Os resultados mostram que, o aumento da área da seção transversal proporciona um aumento na faixa de estabilidade de chama do queimador quando comparado com um de área constante. A eficiência de radiação também é influenciada positivamente pela variação de área, ou seja, um aumento na área da seção de saída do dispositivo resulta em um aumento na eficiência. Também é testada uma modelagem alternativa baseada no método de curvas de nível (level-set method). Nesse modelo as equações das espécies químicas são substituídas pela equação-G, a qual descreve a dinâmica de uma frente de chama infinitamente fina. Os resultados numéricos das simulações bem como as vantagens e as limitações do modelo de curvas de nível são discutidas. Em linhas gerais os resultados do modelo de curvas de nível não foram capazes de reproduzir adequadamente o comportamento obtido com o modelo convencional. / In this work, the premixed combustion of methane and air in a porous radiant burner with a variable cross-sectional area is investigated. The flame stability and the radiant efficiency in this kind of burner are analyzed through numerical simulation. The problem considers a variable area one-dimensional burner with radiation heat losses in its extremities. The numerical method used to solve the set of conservation equations is the finite volume method with the Cartesian coordinate system. The results show that an increase of the cross-sectional area promotes an increase of the flame stability range when compared with a constant area burner. The radiant efficiency is also positively influenced by the area variation, i.e., the increase of the outlet area results in an enhanced efficiency. An alternative modelling based on the level-set method is also tested. In this model the equations of chemical species are replaced by the G-Equation, which describes the dynamics of an infinitely thin flame front. The numerical results of simulations as well as advantages and limitations of the level-set model are discussed. In general the results of the level-set model were not able to reproduce in a suitable way the behavior obtained with the conventional model.

Nesse trabalho, é investigada a combustão pré-misturada de metano e ar em um queimador poroso radiante com área de seção transversal variável. A estabilidade de chama e a eficiência de radiação neste tipo de queimador são analisadas através de simulação numérica. O problema considerado para análise é de um queimador unidimensional de área variável com perdas de calor por radiação em suas extremidades. A metodologia numérica usada para resolver o conjunto de equações de conservação é o método dos volumes finitos com o sistema de coordenadas cartesianas. Os resultados mostram que, o aumento da área da seção transversal proporciona um aumento na faixa de estabilidade de chama do queimador quando comparado com um de área constante. A eficiência de radiação também é influenciada positivamente pela variação de área, ou seja, um aumento na área da seção de saída do dispositivo resulta em um aumento na eficiência. Também é testada uma modelagem alternativa baseada no método de curvas de nível (level-set method). Nesse modelo as equações das espécies químicas são substituídas pela equação-G, a qual descreve a dinâmica de uma frente de chama infinitamente fina. Os resultados numéricos das simulações bem como as vantagens e as limitações do modelo de curvas de nível são discutidas. Em linhas gerais os resultados do modelo de curvas de nível não foram capazes de reproduzir adequadamente o comportamento obtido com o modelo convencional. / In this work, the premixed combustion of methane and air in a porous radiant burner with a variable cross-sectional area is investigated. The flame stability and the radiant efficiency in this kind of burner are analyzed through numerical simulation. The problem considers a variable area one-dimensional burner with radiation heat losses in its extremities. The numerical method used to solve the set of conservation equations is the finite volume method with the Cartesian coordinate system. The results show that an increase of the cross-sectional area promotes an increase of the flame stability range when compared with a constant area burner. The radiant efficiency is also positively influenced by the area variation, i.e., the increase of the outlet area results in an enhanced efficiency. An alternative modelling based on the level-set method is also tested. In this model the equations of chemical species are replaced by the G-Equation, which describes the dynamics of an infinitely thin flame front. The numerical results of simulations as well as advantages and limitations of the level-set model are discussed. In general the results of the level-set model were not able to reproduce in a suitable way the behavior obtained with the conventional model.

Neste trabalho, avaliou-se a queima do sebo bovino por meio de uma fornalha calorimétrica flamotubular instrumentada que opera à pressão atmosférica. Como parte do trabalho experimental, foram analisadas as curvas de rendimento térmico da queima do combustível, sebo bovino, e verificou-se seu comportamento quanto à transferência de calor e emissão de gases. Experimentalmente, a fornalha calorimétrica foi remodelada e adaptada para operar com sebo bovino, incorporando-se a esta um elemento de aquecimento prévio, trata-se de um queimador desenvolvido no NETeF possuindo um sistema de alimentação com aquecimento para o combustível, já que o sebo se encontra no estado sólido a temperatura ambiente. O queimador utilizado no experimento foi do tipo misto. Os resultados das medições do poder calorífico do sebo bovino mostraram-se altos: 39.985,5 kJ/kg (dados obtidos no laboratório do NETeF), fazendo com que o sebo se torne uma fonte menos poluente. / In this study, we evaluated the burning of tallow by a calorimetric flamotubular instrumented furnace which operates at atmospheric pressure. As part of the experimental work, the curves of thermal efficiency of fuel combustion (beef tallow) were analyzed, and it was possible to set their composition toward the transfer of heat and gas emissions. Experimentally, the calorimetric furnace was remodeled and adapted to operate with beef tallow by incorporating an element of this preheating, it is a burner developed in NETeF and it has a system to supply heating for fuel, as the tallow is solid at room temperature. The burner used in the experiment was of mixed type. The results of measurements of the calorific value of beef tallow were shown to be high: 39985.5 kJ/kg (data obtained in the laboratory of NETeF), causing the fat to become a viable source.

Este trabalho apresenta os estudos técnicos para implantação de um sistema de geração de energia que atenda a demanda dos circuitos eletroeletrônicos de um queimador de biogás, tornando-o autossuficiente energeticamente e viabilizando sua instalação em locais distantes e não atendidos pelo sistema convencional de distribuição de energia. O projeto do sistema de geração de energia tem como base a associação das tecnologias fotovoltaica e termoelétrica direta, tipo efeito Seebeck. O queimador de biogás descrito neste projeto é instalado em miniestações de tratamento de efluentes com produção de biogás, onde o aproveitamento energético da forma tradicional é inviável em função da baixa e inconstante vazão de biogás. O queimador de biogás possui um circuito eletrônico de controle que determina o tempo de combustão do biogás, onde, através de um microcontrolador, recebe informações do circuito eletrônico de controle e registra o volume de biogás queimado, objetivando a obtenção dos créditos de carbono. O queimador de biogás tem como objetivo somente o saneamento, provocando a queima do gás metano (CH4) presente no biogás e permitindo a busca por créditos de carbono, contribuindo para a diminuição dos efeitos provocados pelos gases do efeito estufa (GEE). Durante os estudos, foi constatado que a energia gerada pelo painel fotovoltaico é suficiente para atender a demanda de energia do circuito eletroeletrônico do queimador de biogás, enquanto que o sistema termoelétrico direto obteve resultados desprezíveis. Constatou-se também que parte do circuito do controlador de carga, utilizado nesse estudo, pode futuramente ser inserida no firmware do microcontrolador já existente no projeto, reduzindo assim significativamente os componentes do circuito. / This paper presents the technical studies for the implementation of a system of power generation to meet the energy demand of biogas burner electronics circuits, making it self-sufficient energy and enabling installation in remote locations not served by the conventional system of energy distribution. The design of the power generation system is based on the combination of photovoltaic technologies and thermoelectric direct like Seebeck Effect. The biogas burner described in this project is installed in mini-stations for treatment and biogas production, where energy reuse in the traditional way is not feasible due to the low and variable flow of biogas. The biogas burner has an electronic control circuit which determines the time of combustion of biogas, which, through a microcontroller receives information from the electronic control circuit and registers the volume of biogas flared aiming to get carbon credits. The biogas burner, aims only sanitation, causing burning methane gas (CH4) present in biogas and allowing the search for carbon credits, helping to reduce the effects caused by greenhouse gases (GHG). During the studies, it was found that the energy generated by the photovoltaic panel is enough to attend the energy demand of the electronics circuit of biogas burner, while the direct thermoelectric system obtained a negligible result. It was found that part of the charge controller, used in this study, in the future can be inserted into the firmware of the microcontroller existing of the in the project, reducing therefore the circuit components significantly.

The topic of this thesis is the calculation of the steam-boiler. The begining of the thesis deals with stoichiometric calculations. In the second chapter is performed the heat balance of the boiler. In the fourth and fifth chapter are defined dimensions of the fire and is established the temperature of a combustion gas in the outlet from the fire. The fifth chapter includes the balance calculations of the particular heating surfaces of the steam-boiler. As a conclusion of the calculations of the steam-boiler is performed the total balance. In the last chapter are proposed the methods for a reduction of the quantity of NOx contained in the combustion gas.

Im Rahmen der Dissertation wurde ein vollkeramischer Porenbrenner entwickelt, der im Bereich hoher Prozesstemperaturen eingesetzt werden kann. Die Brennerentwicklung umfasste die Entwicklung und Auswahl von geeigneten Komponenten wie ein Gehäuse und eine Flammensperre sowie die Anpassung an die Brennergeometrie. Die entwickelten Porenbrenner wurden Tests im Freibrand und im Hochtemperaturofen im Labor unterzogen. Eine entscheidende Rolle für die Bewertung des Brennersystems spielte die Qualifizierung unter Realbedingungen. Das Brennersystem wurde in Ofenanlagen zur Glasherstellung eingesetzt. Durch die Versuche in einer Arbeitswanne für die Herstellung von Behälterglas und in einer Vorwärmtrommel für die Herstellung von Kunstglas wurde der Nachweis der Industrietauglichkeit erbracht. Es wurden dabei die Vorteile wie Energieeinsparnis, verbesserte thermische Homogenität und niedrige CO- und NOx-Emissionen gezeigt.

Every computational fluid dynamics engineer deals with a never ending story – limitedcomputer resources. In computational fluid dynamics there is practically never enoughcomputer power. Limited computer resources lead to long calculation times which result inhigh costs and one of the main reasons is that large quantity of elements are needed in acomputational mesh in order to obtain accurate and reliable results.Although there exist established meshing approaches for the Siemens 4th generation DLEburner, mesh dependency has not been fully evaluated yet. The main goal of this work istherefore to better optimize accuracy versus cell count for this particular burner intended forsimulation of air/gas mixing where eddy-viscosity based turbulence models are employed.Ansys Fluent solver was used for all simulations in this work. For time effectivisationpurposes a 30° sector model of the burner was created and validated for the meshconvergence study. No steady state solutions were found for this case therefore timedependent simulations with time statistics sampling were employed. The mesh convergencestudy has shown that a coarse computational mesh in air casing of the burner does not affectflow conditions downstream where air/gas mixing process is taking place and that a majorpart of the combustion chamber is highly mesh independent. A large reduction of cell count inthose two parts is therefore allowed. On the other hand the RPL (Rich Pilot Lean) and thepilot burner turned out to be highly mesh density dependent. The RPL and the Pilot burnerneed to have significantly more refined mesh as it has been used so far with the establishedmeshing approaches. The mesh optimization has finally shown that at least as accurate resultsof air/gas mixing results may be obtained with 3x smaller cell count. Furthermore it has beenshown that significantly more accurate results may be obtained with 60% smaller cell count aswith the established meshing approaches.A short mesh study of the Siemens 3rd generation DLE burner in ignition stage of operationwas also performed in this work. This brief study has shown that the established meshingapproach for air/gas mixing purposes is sufficient for use with Ansys Fluent solver whilecertain differences were discovered when comparing the results obtained with Ansys Fluentagainst those obtained with Ansys CFX solver. Differences between Fluent and CFX solverwere briefly discussed in this work as identical simulation set up in both solvers producedslightly different results. Furthermore the obtained results suggest that Fluent solver is lessmesh dependent as CFX solver for this particular case.

This thesis describes the phase and amplitude correction of 12.7 mm diameter, Type-1 microphones for three frequency bands, including within the infrasound regime, and its application to acoustic measurements. Previous data stem from acoustic intensity measurements using two-dimensional, four-microphone probes, which emphasized the requirement of having the acoustic phase and amplitude difference be much greater than the interchannel mismatch. Although correcting the amplitude/phase is well-known, obtaining the necessary transfer functions in the infrasound regime is challenging because (1) signal-to-noise ratios are often poor, (2) long measurement times are required for averaging, and (3) microphone responses vary significantly across these low frequencies. In this paper, a convenient infrasound source previously studied for infrasound adverse effects on humans is intended for performing a relative calibration. This work also seeks to elaborate recommendations for probe spacing, averages or length recordings, and instrument mismatch. The last two chapters show the PAGE method application in infrasonic sources. Those chapters have the intensity measurements using free-field microphones with larger separation distances than commercial intensity probes but compact compared to state of the art in infrasonic arrays.

Oxygen-diluted Combustion (OdC) technology has evolved from the concept of Excess Enthalpy Combustion and is characterized by reactants of low oxygen concentration and high temperature. Recent advances in this technology have demonstrated significant energy savings, high and uniform thermal field, low pollution, and the possibility for downsizing the equipment for a range of furnace applications. Moreover, the technology has shown promise for wider applications in various processes and power industries. The objectives of this thesis are to analyze the thermodynamic aspects of this novel combustion technology and to quantify the enhancement in efficiency and heat transfer inside a furnace in order to explore the potentials for reduced thermodynamic irreversibility of a combustion process and reduced energy consumption in an industrial furnace. Therefore, theoretical and experimental investigations were carried out. The 2nd law of thermodynamics analyses of OdC systems have been carried out for cases in which the oxidizer is either oxygen (Flameless-oxy-fuel) or air (High Temperature Air Combustion, HiTAC). The analyses demonstrate the possibilities of reducing thermodynamic irreversibility of combustion by considering an oxygen-diluted combustion process that utilizes both gas- and/or heat-recirculation. Furthermore, the results showed that an oxygen-diluted combustion system that utilizes oxygen as an oxidizer, in place of air, results in higher 1st and 2nd law efficiencies. Mathematical models for heat regenerators were developed to be designing tools for maximized heat recovery. These models were verified by heat performance experiments carried out on various heat regenerators. Furthermore, experiments were performed in a semi-industrial test furnace. It was equipped with various regenerative burning systems to establish combustion and heat transfer conditions prevailing in an industrial furnace operating based on HiTAC. The tests were carried out at seven firing configurations, two conventional and five HiTAC configurations, for direct and indirect heating systems. Measurements of energy balance were performed on the test furnace at various configurations in order to obtain the 1st law efficiency. Moreover, local measurements of temperature, gas composition, and heat fluxes in the semi-industrial test furnace were performed to find out the main characteristics of HiTAC flame and the effects of these characteristics on the heating potential, i.e., useful heating in the furnace. In the case of HiTAC, these measurements showed uniformities of chemistry, temperature, temperature fluctuation, and heat fluxes profiles. The values of fluctuations in temperature were small. The high speed jets of the fuel and air penetrated deep into the furnace. The fuel gradually disappeared while intermediate species gradually appeared in relatively high concentrations and at broader regions inside the furnace. These findings indicate: a large reaction zone, low specific combustion intensity in the flame, low specific fuel energy release, and high heat release from this large flame. In addition to the thermodynamic limitations to the maximum temperature of the Oxygen-diluted Combustion, the low specific energy release of the fuel and the high heat release from the flame to its surroundings cause this uniform and relatively moderate temperature profile in a HiTAC flame, consequently suppressing thermal-NO formation. Heat flux and energy balance measurements showed that heating potential is significantly increased in the case of HiTAC compared to that in the conventional case, implying much more energy savings than the apparent heat recovery from the heat regenerators, and consequently much less pollutants emissions. Therefore, it is certain that this large HiTAC flame emits more thermal radiation to its surroundings than the conventional flame does, in spite of the moderate-uniform temperature profile of the flame. This intense heat flux was more uniform in all HiTAC configurations, including the indirect heating configuration, than that of the conventional-air combustion configuration. / QC 20101011